Mike, they are pretty str8 forward...just takes a little time so I’d say a 2-3.
Mike, I have one old Benjamin hand pump that dates back to 2013. It has been in continuous use during those years - so it has been taken apart several times to replace o-rings. After all that practice, I can disassemble, clean, change what is worn, lubricate, and reassemble in about 30 minutes. Bingo! I am back in business. Basic tools are all that is required along with a little perseverance. (Don't try to over-tighten things when reassembling. Snug usually works.)